1. Field of the Invention
The present invention generally relates to a print hammer control device, and more particularly to a device for controlling print hammer speed immediately before a print hammer impinges on a print wheel.
2. Description of the Prior Art
There has been known printing devices, such as print wheel electric typewriter, capable of printing and erasing characters. Such a printing device has a carriage on which print hammer, print wheel, ink ribbon, erase ribbon and their drive mechanisms are mounted. In the electric typewriter, printing is carried out with a print hammer. The print hammer is moved at a high speed by a print hammer drive mechanism so as to impinge on the print wheel, thereby making a character impression on a sheet of paper. In such a printing device, it is required that the print wheel be applied with a predetermined pressure to maintain a standard level of print quality. To this end, both print hammer position and print hammer speed are detected by a combination of a computer and an encoder so that the print hammer speed is controlled based on the detected data.
However, in order to detect the speed and position of the print hammer during a high speed movement thereof, a high resolution encoder and a high performance CPU are required. The high resolution encoder is necessary to obtain precise data, and the high performance CPU is necessary because the CPU has to accomplish the speed control of the print hammer within an extremely short period of time immediately before the hammer impinges on the print wheel. A problem then arises due to expense of the complex equipment needed.